Visual Acuity Research

Measuring visual acuity is important in the optometry field and one of the easiest tests to be performed. It can also be a good indicator for the presence or absence of refractive error and monitoring the progression of ocular diseases. If there is reduction of visual acuity after the refraction is performed, it will give us a signal to find out the reason of the underlying causes. Nowadays, most of the optometrist used Snellen Chart for the measurement of visual acuity. However, it is well known that Snellen Chart have several disadvantages because the chart was not standardized. To overcome the problem, the Australian Optometrists, Ian Bailey and Jan Lovie come out with an idea to develop the Bailey Lovie logMAR visual acuity Chart in 1976

Some of the modifications are reduced five letters to two letters per line, reduced the spacing between letter (crowding effect) and eccentric fixation. Crowding phenomenon occurs when a letter is surrounded by the other letter and caused the visual acuity to reduce compared to visual acuity measured using a single letter. By performing Modified logMAR chart, this phenomenon is more enhanced because the target is presented eccentricity than central fixation. Flom et.al (1991) reported that, contour interaction of letter occurs at a level higher than the retina which is at the occipital cortex and results in the lateral inhibition of the cortex. Other than that, in this research we are mimicking the amblyopic condition on the normal healthy individual. In normal people, the high density of cones at the fovea is important for the higher level of visual acuity in photopic condition. For the eccentric fixation, the fovea is located at 5 minute of arc from center of fixation. Therefore, there will be 25% loss of visual

Other than that, this chart can also reduce the time taken for the measurement of visual acuity. Amblyopia is also known as lazy eyes. According to American Optometry Association (AOA), amblyopia is defined as loss or lack of development of central vision in one eye that is unrelated to any eye health problem and is not correctable with lenses. Amblyopia which occur 3%-5% is the major public health issue. It can be unilateral or bilateral and have best corrected visual acuity less than 6/6. There are several type of amblyopia for example; Strabismic Amblyopia, Anisometropic Amblyopia, Meridional Amblyopia and Bilateral Refractive Amblyopia. The major concern for this research is about Strabismic Amblyopia because it is related with the eccentric fixation. Based on the current studies, 51% of children with esotropia were found to have amblyopia compared to exotropia which is 14% (Mohney, 2001 and Mohney&Huffaker, 2003). Because of the relationship between strabismic and amblyopia, it is important to diagnose strabismus as soon as possible in order to reduce the risk of amblyopia (von Noorden